Implement --no-update-modtime flag - fixes #511

docs/content/docs.md

@@ -560,6 +560,14 @@ uploaded compressed files.
 There is no need to set this in normal operation, and doing so will
 decrease the network transfer efficiency of rclone.
 
+### --no-update-modtime ###
+
+When using this flag, rclone won't update modification times of remote
+files if they are incorrect as it would normally.
+
+This can be used if the remote is being synced with another tool also
+(eg the Google Drive client).
+
 ### -q, --quiet ###
 
 Normally rclone outputs stats and a completion message.  If you set

fs/config.go

@@ -89,6 +89,7 @@ var (
 	maxDepth        = pflag.IntP("max-depth", "", -1, "If set limits the recursion depth to this.")
 	ignoreSize      = pflag.BoolP("ignore-size", "", false, "Ignore size when skipping use mod-time or checksum.")
 	noTraverse      = pflag.BoolP("no-traverse", "", false, "Don't traverse destination file system on copy.")
+	noUpdateModTime = pflag.BoolP("no-update-modtime", "", false, "Don't update destination mod-time if files identical.")
 	bwLimit         SizeSuffix
 
 	// Key to use for password en/decryption.
@@ -240,6 +241,7 @@ type ConfigInfo struct {
 	MaxDepth           int
 	IgnoreSize         bool
 	NoTraverse         bool
+	NoUpdateModTime    bool
 }
 
 // Transport returns an http.RoundTripper with the correct timeouts
@@ -345,6 +347,7 @@ func LoadConfig() {
 	Config.MaxDepth = *maxDepth
 	Config.IgnoreSize = *ignoreSize
 	Config.NoTraverse = *noTraverse
+	Config.NoUpdateModTime = *noUpdateModTime
 
 	ConfigPath = *configFile
 

fs/operations.go

@@ -147,7 +147,7 @@ func Equal(src, dst Object) bool {
 		return false
 	}
 
-	if !Config.CheckSum {
+	if !(Config.CheckSum || Config.NoUpdateModTime) {
 		// Size and hash the same but mtime different so update the
 		// mtime of the dst object here
 		err := dst.SetModTime(srcModTime)

fs/sync_test.go

@@ -311,6 +311,25 @@ func TestSyncAfterChangingModtimeOnly(t *testing.T) {
 	fstest.CheckItems(t, r.fremote, file1)
 }
 
+func TestSyncAfterChangingModtimeOnlyWithNoUpdateModTime(t *testing.T) {
+	r := NewRun(t)
+	defer r.Finalise()
+	fs.Config.NoUpdateModTime = true
+	defer func() {
+		fs.Config.NoUpdateModTime = false
+	}()
+
+	file1 := r.WriteFile("empty space", "", t2)
+	file2 := r.WriteObject("empty space", "", t1)
+
+	fs.Stats.ResetCounters()
+	err := fs.Sync(r.fremote, r.flocal)
+	require.NoError(t, err)
+
+	fstest.CheckItems(t, r.flocal, file1)
+	fstest.CheckItems(t, r.fremote, file2)
+}
+
 func TestSyncAfterAddingAFile(t *testing.T) {
 	r := NewRun(t)
 	defer r.Finalise()